U.S. patent number 4,105,561 [Application Number 05/547,454] was granted by the patent office on 1978-08-08 for directional filter.
This patent grant is currently assigned to Domnick Hunter Engineers Limited. Invention is credited to Keith R. Domnick.
United States Patent |
4,105,561 |
Domnick |
August 8, 1978 |
Directional filter
Abstract
A filter having a microporous filter sleeve formed from fibres
providing pore sizes below 50 microns, supported by a rigid
support, and held at each end in a tapered channel in an end cap to
compress the end zones of the sleeve. The end caps can be urged
towards each other by a tie rod, extending between them, having a
nut and screw arrangement. A porous sock may be provided downstream
of the filter element, and this can be of plastic material, or of
foamed metal, and combined with the rigid support.
Inventors: |
Domnick; Keith R. (East Boldon,
GB2) |
Assignee: |
Domnick Hunter Engineers
Limited (GB)
|
Family
ID: |
9827824 |
Appl.
No.: |
05/547,454 |
Filed: |
February 6, 1975 |
Foreign Application Priority Data
|
|
|
|
|
Feb 16, 1974 [GB] |
|
|
7163/74 |
|
Current U.S.
Class: |
210/232; 210/444;
210/489 |
Current CPC
Class: |
B01D
17/045 (20130101); B01D 46/0024 (20130101); B01D
46/0031 (20130101); B01D 46/2414 (20130101); B01D
2271/027 (20130101) |
Current International
Class: |
B01D
46/24 (20060101); B01D 17/04 (20060101); B01D
025/02 () |
Field of
Search: |
;210/489,509,444,497,232 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spear, Jr.; Frank A.
Claims
What I claim is:
1. A filter device comprising in combination: a self-supporting
tubular microporous layer of a filter medium wherein the filter
medium includes fibers providing a plurality of pores within a
range of pore sizes substantially less than 50 microns; a binding
material reinforcing said fibers; end caps of which each end cap
defines an annular channel within a wall face thereof; one of said
caps being at one end and another of said caps being at an opposite
end of the tubular microporous layer mounted thereon; each end of
the tubular microporous layer being held in a respective one of
said annular channel against the channel-defining wall face
thereof, of the end caps at opposite ends of the tubular
microporous layer; each end cap comprising at least one impermeable
member, each channel having a tapering cross-section which
constricts towards a floor of the annular channel, adapted such
that on assembly, end regions of the tubular microporous layer are
compressed within the channels against the channel-defining wall
faces of the end caps; and the filter medium layer forming an
impermeable compression seal with the respective channel-defining
walls of the end caps.
2. A filter device of claim 1, in which at least one side wall of
each annular channel is inclined, adapted such that
longitudinally-directed pressure on the tubular microporous layer
is converted into laterally-directed compression of walls of the
tubular microporous layer.
3. A filter device of claim 2, in which a tie rod is mounted onto
and between the end caps and provide axial longitudinally-directed
compression force between the end caps, the tie rod being secured
at one end to said one end cap and passing through said other end
cap at an opposite and threaded end of the tie rod, with a nut
screw mounted on the threaded end and adapted to urge the two end
caps together toward one-another sufficiently to compress the
tubular microporous layer.
4. A filter device of claim 1, in which the tubular micro-porous
layer includes reinforcement structure on the normally upstream
side thereof.
5. A filter device of claim 4, in which said reinforcement
structure includes a coil spring with a natural outside diameter
at-least greater than inside diameter of the tubular microporous
layer.
6. A filter device of claim 5, in which a post-filter layer is
mounted in flow series downstream of the tubular microporous
layer.
7. A filter device of claim 6, in which the post-filter layer
comprises an open-pored plastic-foam sock.
8. A filter device of claim 6, in which the tubular microporous
layer and the post-filter layer are combined into a single one
structure, in which the tubular micro-porous layer is formed from
open pored metal foam of tubular shape and encloses and supports
the post-filter down-stream and is adapted to trap any coalesced
droplets of liquid.
9. A filter device of claim 1, in which the tubular microporous
layer has a pore size of from about 1 to about 7 microns.
10. A filter device of claim 1, in which the tubular microporous
layer has a pore size of from about 7 to about 11 microns.
11. A filter device of claim 1, in which the filter tube has a pore
size of from about 11 to about 24 microns.
Description
This inventions relates to improved filters of the kind comprising
a microporous sleeve of filter medium, held in a sealed
relationship with a housing, for the removal from fluid of
particles and droplets of liquid having sub-micronic
dimensions.
It has been proposed to clamp the ends of a tube of filter medium
against end caps, with or without the interdisposition of gaskets
or washers, for sealing the ends, and thus constraining the fluid
to pass through the filter medium, and this has been proved
adequate in the case of coarse filters e.g. having a filter medium
retaining particles having dimensions of 50 microns and greater,
but for finer discrimination e.g. for retaining particles having
dimensions of 10 microns or less, and particularly of dimensions
less than 1 micron, channelling takes place between the filter
medium and the end cap or gasket causing errosion at the filter
medium boundary and premature failure resulting in unfiltered fluid
by-passing the affected filter medium.
According to the invention a filter comprises a tubular microporous
layer of filter medium where the filter medium employs fibres
providing a multiplicity of pores in a range of sizes substantially
less than 50 microns, and which are reinforced with a binding
material, the tubular layer of filter medium being held, in use,
with the free end regions constrained in corresponding channels
formed in or by at least one impermeable member at each end region
at least partially defining a fluid flow path through the filter
layer, the free end regions of the tubular layer of filter meduim
being compressed when assembled in the channels whereby the filter
layer forms an impermeable compression seal with the walls of the
channels.
At least one side wall of each annular space is preferably inclined
and the free ends of the filter layer are preferably
correspondingly inclined on the inner and/outer edges whereby an
even fit is provided round the periphery of each end region when
assembled and a longitudinal pressure in the filter tube is
converted into a lateral compression of the filter tube wall.
The impermeable members preferably comprise a first end cap for
closing one end of the filter tube and a second end cap having a
port for fluid flow communicating with the interior of the filter
tube when the second end cap is held against the other end of the
filter tube.
It is an advantage of the invention that new end caps are not
required in the provision of a replacement filter cartridge
whenever the filter medium is replaced nor is the operation of
sealing end caps to the filter medium necessary in the production
of the filter cartridge. These measures also permit the production
of an inexpensive filter cartridge and, in addition, a support for
the filter medium layer may be provided as a part of the filter
rather than it being necessary to incorporate the support, or
supports, in the replacement filter cartridge.
A support for the filter medium is preferably located downstream of
the filter medium in use and may be formed from perforated or
expanded metal sheet material, for example, 26 gauge stainless
steel or brass or cadmium coated mild steel and a further porous
tube, e.g. an opened pored plastics foam sock is preferably
employed as a postfilter to retain coalsced liquid droplets, for
instance coalesced oil mist and condensed water vapour, downstream
of the support.
The functions of the support tube and post-filter layer may be
combined in one structure which is formed from an open pored metal
foam in a tubular shape to enclose and support the filter tube
downstream of the filter, in use, and also trap any coalesced
droplets of liquid. The metal foam tube, preferably has a flexable
gasket at each end seal the tube to the end caps.
In use it is preferable to employ a pre-filter, i.e. a fluid filter
of coarser grade to remove larger particles which would tend to
quickly clog the microporous filter layer and thus reduce its
operating life. This pre-filter may be mounted in the same filter
body as the microporous filter elements and is preferably of
tubular form with an end cap which may or may not be permeable, and
may be mounted coaxially of the microporous filter element upstream
of the fluid flow in use, i.e. inside or outside the microporous
filter tube depending on the normal direction of fluid flow.
A tie rod is preferably employed for providing an axial
longitudinal compression force between the end caps. The tie rod
may be secured at one end to one of the end caps passing through
the other end cap, when assembled, with a nut screw engaged by a
screw thread on the tie rod for urging the two end caps together
and thus compressing the filter tube. A gasket is preferably
employed between the nut and the end cap to enable a fluid tight
seal to be obtained. Alternatively or in addition the tie rod may
be secured to the filter housing passing, in use, through both end
caps and having a nut screw engaged by a screw thread on the remote
end for urging the end cap axially towards the filter housing. The
embodiment with the tie rod secured to one end cap may be made up
as a seperate filter cartridge which may be pre-assembled and
secured in the filter housing at a later time by means of screw
threaded or other coupling means.
Where high reverse pressure loadings are likely to be encountered,
the microporous filter layer is preferably reinforced on the
normally upstream side, for instance by a coil spring with a
natural outside diameter slightly greater than the inside diameter
of the filter tube.
The liquid aerosol droplets coalesced into bulk liquid on impact
with the filter fibres and this bulk liquid is carried by the fluid
flow through to the outer surface of the filter layer where it
appears at randomly distributed points. The much greater pore size
of the post-filter layer allows the bulk liquid carried off the
microporous filter layer to seep down to the bottom of the foam
layer where it forms a wet band, the excess liquid dropping off the
filter assembly into a sump in the filter body from where it may be
drained manually or automatically.
The porous material for the post-filter layer preferably has a high
surface area for its volume, for instance the polyurethane and
aluminium foam tubes have a surface area of approximately 2,000 sq.
ft. per cubic foot.
The fibres employed in the filter medium layer are such as to
provide the latter with a multiplicity of pores having a dimension
in ranges of up to 50 microns and may be resin-reinforced by curing
a pad of fibres impregnated with reinforcing resins such as epoxy
or formaldehyde resin; the fibres may have diameters in ranges of
up to 4 microns. The surface of the element normally in contact
with the end caps is preferably moulded to obtain a high standard
of surface smoothness.
The filter medium body, which is usually cylindrical, may be
provided in several ranges of porosity for varying requirements,
for example, a fine pores size having pores with a dimension in the
range of 1 to 7 microns, intermediate pore sizes having pores in
respective ranges of from 7 to 11 and of 11 to 24 microns and a
small pore size having pores in the range of from 24 to 40
microns.
The fibres of the filter medium body are preferably non absorbent,
i.e. fibres or chopped filaments having a low moisture regain
usually less than 1.5% and preferably glass, e.g. borosilicate,
fibre. The fibre must be very fine, but it is not necessary that
the majority of the fibres are of the same order of size as the
contaminent particles retained or the droplets which coalesced on
them.
The fibres diameters of the filter medium body of fine pore size
are preponderantly of the order of 0.5 microns, those of the filter
medium bodies of intermediate pore size being preponderantly of
respective orders of 1 and 2 microns whilst the fibre diameters of
the filter medium body of small pores size having pores in the
range of from 24 to 40 microns are preponderantly of the order of 4
microns.
It has been found that a filter medium cylinder of the small pores
size removes 91% of contaminants having diemsions in the range of
0.05 to 2 microns whilst the filter medium sleeves having finer
pores sizes remove over 99% of such contaminants, the fine pores
size filter medium sleeve effecting virtually complete removal of
99.999%.
Preferred embodiments of the invention will now be described by way
of example, with reference to the accompanying drawings,
wherein;
FIG. 1 is a sectional view of a filter housing incorporating a
first embodiment of filter according to the invention;
FIG. 2 is a similar sectional view, showing a second embodiment of
filter according to the invention;
FIG. 3 is a diagrammatic partial sectional view illustrating a
third embodiment of the filter according to the invention;
The filter shown in FIG. 1 comprises a bullet shaped filter housing
1, secured, by a collar 2 to an inlet and outlet head 3, having an
inlet passage 4 and an outlet passage 5 defined therein. A filter
cartridge is mounted in the head 3 by means of a screw threaded
boss 6 formed on an upper end cap 7 of the cartridge. The boss 6
has windows 8 which communicate between the inlet passage 4 and the
interior of the boss, and of the filter cartridge. The cartridge
also has a second, blind, end cap 9, which is connected by a tie
rod 10 to the boss 6.
A filter element 11, in the form of a resin bonded microporous
cylindrical sleeve providing a multiplicity of pores in a range
from 11 to 24 microns, or alternatively in one of the ranges
mentioned above is provided extending btween the end caps 7 and 9,
and received in each end cap in a groove 12. The radially outer
face of each groove 12 is inclined, so that the groove is narrower
at its base than at its mouth. This has the effect in assembly,
when the element 11 is pushed into the groove, the end of the
element is compressed, causing the impregnating resin to fill the
pores in the end region of the filter element 11, thus avoiding the
risk of channeling at the ends. A further cylindrical sleeve 13, of
porous formed metal is disposed around the element 11. This sleeve
13 acts as a mechanical support for the element 11 against the
pressure of outward flow of the fluid being filtered from within
the cartridge, to the surrounding space within the housing 1. The
sleeve 13 also acts as a post filter for removing for example
coalesced droplets of oil from the stream passing the filter
element 11. Gasket type seals 14 and 15 are provided between the
ends of the sleeve 13 and the respective end caps 7 and 9.
The tie rod 10 is received in a screw-nut 16, which is rotatable in
end cap 9. Rotation of the nut 16 moves it either towards or away
from the boss 6, thus increasing or decreasing the axial pressure
on the filter element 11, and varying the compression of the ends
of the element 11 in the grooves 12.
In FIG. 2 is shown an embodiment similar to FIG. 1 corresponding
parts having the same reference numbers, wherein the filter element
11, besides being supported on the normally upstream side by the
sleeve 13, is also supported on the normally downstream side by a
coil spring 17, for protection of the filter element 11 against
transient back pressures, which can arise in some phases of
operation of a filter.
FIG. 3 diagrammatically illustrates a third embodiment designed for
flow in the reverse direction through the filter housing, as shown
by the arrows. The filter element 11 is supported internally, that
is on the normally downstream side, by a cylindrical perforated
sheet metal support 18. The support 18 is received at one end in a
special recess in the end cap 7, and is deflected at the other end
where it abuts the end cap 9 to give a degree of resilience to its
support for the filter element 11. In the upper end cap 7, the
filter element is held in a channel defined between the support 18
and the cap 7, whereas a proper channel 12 is provided in the lower
end cap 9. A porous sock 19, which may be of porous sintered metal
or a porous expanded plastics material is provided about the inner
surface of support 18 to act as a post-filter.
Variations can be made to the constructional details of the filters
within the scope of the invention. For example, in FIGS. 1 and 2,
the porous metal sock may be replaced by a perforated sheet metal
or perforated plastics sheet support, and the porous sock which is
optional, may be of expanded plastics. On the other hand, a spring
may be provided on the outside of the FIG. 3 embodiment, to guard
against back pressures, or the spring may be replaced by a second
support, so that the filter element is sandwiched between two
supports, and the filter may then be made capable in functioning in
both flow directions.
* * * * *